Field of the Invention
The present invention relates to an electronic circuit, and more particularly relates to a delay apparatus.
Description of Related Art
Delay cells can be applied to various electronic circuits, such as delay locker loops (DLL) and phase locked loops (PLL). The delay cell can provide precise delay, so that the DLL or the PLL can produce a specific frequency. In order to obtain the maximum locked range of the DLL or the PLL, it is usually required to maximize operable range of the delay cell. Besides, there is a gap between ideal values and actual values of the delay cell due to deviations of manufacturing process, temperature and voltage. In order to make the actual values (actual delay range) cover a variety of values for application, it is necessary to maximize the operation range of the delay cell.
However, the operation range of conventional delay cells is restricted by single current source, so that the operation range is limited. Lower frequencies are satisfied when operating in higher frequencies, and vice versa.